Mainly the prominent furrow - white lips + shape. It's not an exact science though. Most but not all species get gradually easier to ventrally sex when they are over 3"+. At the end of the day, ventral sexing gives you a good idea or a reasonably educated suspicion of the sex, which is confirmed without doubt when you have a moult that you can check.So that ive got an idea ( roughly haha) what makes you guys believe its a female from this photo?
PMSL.....with being in the UK I had no idea who John Bolton is. Just googled him. Yep she has a John Bolton for sure....LOLThe “mustache” above the epigastric furrow. Between the anterior book lungs there is a “line” that runs across, that’s the epigastric furrow. When you look midway and you see a John Bolton looking mustache, it’s female. However if you see a “dot”, male. It takes practice but once you practice enough, it gets easier. I use a 40x lighted magnifier, you can get them on eBay for $3-4.